Aaachooo! Nasal neurons nothing to sneeze at

I fixed a baked potato the other night when my wife was out of town, and it made me sneeze. It isn’t that I am allergic to them. It’s that I like a lot of pepper on them, and the pepper makes me sneeze. It strikes me that sneezing because of pepper is an interesting scientific subject that touches on at least two fields of study: mammalian physiology and botany.

Sneezing, correctly but uncommonly known as sternutation, is a reflex triggered when some of the 5 million neuron receptors in the nasal passageway are triggered. The nasal membrane is also bathed in mucus to help pick up various chemicals. Occasionally it becomes necessary to clear the excess mucus from the passageway, and that’s what a sneeze is for.

It is actually a wonder that we don’t sneeze more than we do. The nose produces 1 to 2 pints of mucus a day. It can secrete more when irritated by either bright light or particulate matter such as virus particles, pollen, dust, dander or, well, pepper. But most of the mucus seems to clear out of the passageway in a less forceful manner. When particulate matter touches the nasal membrane, it causes the release of histamine. That in turn causes blood vessels in the area to dilate and bring in extra fluids. The extra fluid traps more particles until the extra mucus must be dispelled.

Pepper comes from a plant called piper nigrum that is grown mostly in Southern India, Vietnam, Indonesia and other hot humid countries. The active compound in pepper is called piperine. Piperine attaches to specific neurons in the nasal passage. Specifically, it attaches to openings in the cell membrane called ion channels. These then cause the ion channel to open and allow extra mucus to flow. That triggers the sneeze reflex.

Sneezing is a little like reverse swallowing. When swallowing, the back of the tongue is raised. The soft palate also rises, closing the nasal passageway. This action forces food backward into the esophagus. During a sneeze, the soft palate depresses downward while the back of the tongue rises. This partially closes off the mouth opening and leaves the nasal passageway as the main channel out. (Don’t think about this too carefully while you are actually doing it. It can mess everything up.)

At the same time the muscles of the chest cavity and the diaphragm suddenly convulse. Air is forced from the lungs and passes out through the nasal passageway, clearing irritants and excess mucus. Because the mouth doesn’t usually close completely, some air may also pass from this opening too. These particles can be expelled at 100 mph, depending on the size and shape of the particle, the dynamics of each individual’s set of muscles and anatomical structure.

The muscles of the eyes are also distorted during a sneeze so that people close their eyes briefly during the process. As a kid I remember someone (probably my sister) telling me that if I tried to sneeze with my eyes open, my eyes would pop out. That isn’t true.

I know because I tried it when I ate my last potato. I also did some calculations and determined that if we sneeze while driving 70 mph, we would travel about 300 feet with our eyes closed. That thought makes me nervous.

Because life long has been associated with air and breathing, sneezing has sometimes been given significance beyond the physiologic event. Sometimes it was considered a prophetic sign. There are those who considered it a window to the soul. People commonly think that the heart stops when a person sneezes, but it doesn’t. But that is why they say “bless you.” So perhaps it isn’t that strange that black peppercorns were found stuffed in the nostrils of Ramses II, who died in 1213 BC.

I guess it was part of the mummification process. But just the thought of it makes me want to sneeze.

Gary McCallister is professor of biology at Mesa State College.


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